The present invention relates to a safety valve with a mechanical friction means between stationary valve parts and movable valve parts for opening and closing the valve, for damping the valve vibrations. A friction force which acts during opening or closing steps on the movable valve part insignificantly brakes the movement of the valve parts. Thereby oscillations of the movable parts which are caused by vibrations taking place additionally to the opening or closing movement, are damped in their amplitude.
The U.S. Pat. No. 3,848,632 discloses a spring-loaded excess pressure valve with a mechanical friction means for damping the valve vibrations. In this valve a valve shaft movable with a valve closing body has a groove which is in open communication with a medium pressure prior to the valve and accommodates an elastic O-ring which under the action of the medium pressure frictionally abuts against a cylindrical wall of a stationary guiding sleeve. This construction possesses the disadvantage that in the event of very small vibration amplitudes, for example of several tenths of millimeters, the O-ring also elastically performs these vibration movements. Therefore only small inner fulling work of the elastic material and not the high friction force acts in this case so that the vibration damping is low. Moreover, this safety function of this valve is in question when the O-ring is "seized" with the abutting cylindrical wall of the stationary guide sleeve, for example when the valve does not operate for a long time.
In addition, the known O-ring is more or less strongly clamped between the lateral walls of the annular groove by the medium pressure, therefore it cannot be determined which part of the outer braking force of the medium is absorbed by the lateral walls and which part is finally transmitted as a friction force to the friction counter surface. Also, the friction action of this O-ring in the valve of greater nominal widths and/or higher pressure is smaller. and this can lead to overheating because of the small mass of the O-ring. Because of tolerances in hardness and temperature action, a constant friction force of the O-ring is also questionable.
The German Auslegeschrift No. 2,654,077 discloses a spring-loaded pressure limiting valve which has an abutment member provided for adjusting of tensioning of the valve spring and a guide rod connected with a movable valve plate and extending through an opening of the abutment member, wherein the abutment member and the guide rod are tilted relative to one another in frictional manner. The tilting of the abutment member and the guide rod is performed under the action of an adjustment screw eccentrically engaging the abutment. With this friction means, the valves can no longer open when the guide rod is seized in the abutment and/or in upper or lower guide bearings because of the tilting. Moreover, because of unavoidable manufacturing play in the opening of the abutment and the guide rod different surface pressure takes place during inclination and in the event of high surface pressure high wear takes place on the friction faces and in the bearings of the guide rod because of the transverse forces acting during the inclination. Thereby a constant friction force is not guaranteed.
In addition, in this known friction means the guide rod is always somewhat inclined because of the tilting, so that the closing member which is fixedly connected therewith either provides for an insufficient closing or must be formed resilient. Also, the tilting can be unintentionally reduced or increased under the action of transverse forces which take place in the valve flow.